1. Field of Use
The present invention relates generally to the removal of solid masses from body passages. More particularly, the invention relates to a stent for expelling stones and their fragments from luminal passages of the human body.
Lithiasis is a common human ailment characterized by calculi or "stones" formed within a passage of the human body. While stones have been documented in just about every passage within the body, kidney stones (nephrolithiasis) and gallstones (cholelithiasis) remain the most common. Regardless of location, however, a stone is typically an extremely hard and unyielding mass which blocks the passage in which it presents.
Kidney stones typify the pathogenesis of stones. These stones, which include calcium or other particulate matter, form hard, irregular masses within the renal calyces or pelvis. Responding to normal urinary flow and pressure, these stones attempt to pass from the kidney, through the ureter, into the urinary bladder, and eventually out through the urethra. Usually, however, the stones cause blockage of the urinary tract producing renal colic with accompanying severe pain.
Most stones will eventually pass. To facilitate the process, though, lithiasis patients often receive intravenous hydration (leading to increased urine output) and parenteral analgesics. As a result of regular peristaltic contractions of ureteral muscles, a stone is usually pushed or flushed outward.
The process may become complicated however. As the stone rubs back and forth (under the influence of peristaltic waves), the delicate lining (endothelium) of the ureter is disrupted. Accompanying swelling or edema effectively reduces the size of the ureteral lumen and impedes or even prevents the passage of the stone. In addition, stones which are relatively large (greater than 0.5 cm) or irregularly shaped frequently become trapped.
Stones which do not pass spontaneously require further intervention. In the past, surgical or other invasive intervention was commonly employed for such stones. Modern treatment, however, favors less invasive or non-invasive modalities. Extracorporeal shockwave lithotripsy, for example, is a non-invasive treatment where sonic or shockwaves are employed to crush calculi into smaller fragments which may then be passed. Other known forms of lithotripsy include ultrasonic, electrohydralic, and laser lithotripsy.
A major impediment to the widespread use of these and other fragmenting techniques has been the elimination of stone fragments from the urinary tract. One approach to this problem has been the use of stents or small catheters to facilitate the passage of fragments while maintaining the patency of the lumen so that urine may pass. In typical use, a stent is placed by cystoscopic technique within the ureter of interest. Once in position, the stent facilitates the passage of the stone fragments by providing a larger passage and, hence, one with less resistance.
The operation of current stents is far from perfect however. Most stone fragments tend to aggregate along side of a stent instead of going through the stent. The fragments, which are trapped between the stent and the endothelium, constantly roll back and forth with movement, including peristalsis, of the urinary tract. This Sisyphean motion further disrupts the delicate endothelial lining of the ureter and leads to increased edema. In fact, the back-and-forth fashion in which conventional stents move stones may actually impede caudal passage of stone fragments.
Thus, it is desirable to provide improved apparatus and methods for the removal of masses (e.g., stones and stone fragments) from body passages, such as the urinary and biliary tracts. The stent should be suitable for introduction to a desired location within a passage, preferably utilizing conventional placement techniques (e.g., cystoscopy, endoscopy, and the like). In addition to maintaining the patency of the passage, the stent should also actively facilitate the expulsion of masses outward from the passage. Furthermore, the stent should minimize trauma to the surrounding tissue and should be suitable for placement for extended periods of time. The present invention fulfills this and other needs.
2. Description of the Background Art
U.S. Pat. No. 4,295,464 describes a ureteric stone extractor comprising a relatively large outer dilator catheter with an inner dislodger catheter slideably disposed within. The inner catheter is provided with a balloon which is inflated once the inner catheter is positioned beyond the arrested stone. Nylon strings positioned along longitudinal axes of the balloon are used to entrap the stone and dislodge it from the ureteral wall.
U.S. Pat. No. 4,690,672 describes a catheter having a mouth in communication with a suction duct and a tongue projecting beyond the mouth; the tongue includes a nozzle aperture for training a jet of fluid into the mouth.
U.S. Pat. No. 4,469,100 describes a double lumen catheter for removing foreign bodies such as a ureteral stone from a body passage. The catheter includes a suction lumen which opens at a distal end and a pressure applying lumen which is open to the interior of the balloon. After placement, the catheter is slowly withdrawn causing intussusception of the distal end of the balloon, thereby surrounding the stone.
U.S. Pat. No. 4,243,040 describes a stone extracting device having an inflatable sleeve attached at the distal end of a tube. When the sleeve is inflated, the distal end of the sleeve is turned inside out and forms a soft annular flaring for engaging a stone. The stone may be captured by suction applied through an inner tube.
U.S. Pat. No. 4,790,812 describes a catheter which includes a parachute basket. A target object is fragmented by a cutting tip at the distal end of the catheter; the parachute basket is deployed downstream of the target object for capturing any fragments which are not aspirated into the catheter lumen.
U.S. Pat. No. 4,883,458 describes an arthrectomy catheter and guidewire for removing an obstruction from within a vessel; the guidewire may include a distal barrier in the form of an umbrella for countering the distal movement of surrounding obstruction material.
U.S. Pat. No. 4,601,713 describes a variable diameter catheter which may be used as a "kidney tube" for excavating stones.
The disclosures of each of the foregoing patents are hereby incorporated by reference.